New York City owns a creepy island that almost no one is allowed to visit — here's what it's like

North Brother Island is hidden in one of the busiest cities in the world. Google Earth; Business Insider

Less than a mile from Manhattan — one of the priciest and most densely populated places on Earth— exists a little-known island that people abandoned nearly 55 years ago.

"North Brother Island is among New York City's most extraordinary and least known heritage and natural places," wrote the authors of a recent University of Pennsylvania study about the location.

The city owns the 22-acre plot of land in the East River, which sits between the South Bronx's industrial coast and Rikers Island Correctional Center — New York City's most infamous jail.

Almost no one is permitted on North Brother Island and its smaller companion, South Brother Island, except for birds. But even they don't seem to want to live among its crumbling, abandoned structures (and contrary to Broad City's depiction of the island, there is no working package pick-up center).

But Business Insider recently took a tour as part of a Science Channel TV shoot, whose producers obtained permission from the city to go.

Here's what we saw and learned while romping around one of New York's spookiest and most forgotten places.

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The only way to get to North Brother Island is by boat. Leaving from Barretto Point Park in the South Bronx is one of the quickest to get there.

This small aluminum boat was our ride.

The East River was crawling with police, probably because Rikers Island Correctional Institute is less than a mile away — and they are wary of anyone visiting North Brother Island.

Google Earth Pro; Business Insider

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No one is permitted to visit the island without permission from the New York City Department of Parks and Recreation, which manages the site as a bird sanctuary. One of their escorts also has to tag along.

The island's buildings used to be powered by coal, which workers loaded onto this dock. Now it's sinking, covered in kelp, and totally submerged at high tide.

Sea levels could rise by as much as 2.5 feet in the next 35 years around New York City. If and when a large hurricane rolls through as the waters rise, the surges will swallow the island's habitats, ecology, structures, and history.

But signs of illegal visitation are peppered about, including this graffiti on a wall ball court.

Some facilities are almost unrecognizable. Ivy has completely choked out this double tennis court.

Rather than take the ferry each day, some hospital workers opted to live in the Nurse's Home. Bath tubs have fallen through the ceiling of the 40,000-square-foot Victorian-style mansion, which was built in 1905.

The structures, like this Physician's Home, built in 1926, are on the verge of collapse. They were probably once beautiful, and might have even been useful today — had they been maintained.

The island struggled to find its purpose after a tuberculosis vaccine emerged in 1943, and soldiers found places to live on the mainland.

The island tried to reinvent itself as a rehabilitation camp for troubled teens, from 1952 through 1963. But patients didn't get the help they needed when returning home after three- to five-month stays. The program was considered a failure.

Everyone left in 1963, and the city took custody of the island. A lack of management made it a looting grounds for vandals. To this day, the city has yet to figure out if and how it will let the public set foot there again.